This application claims the benefit of the Korean Application Nos. P2001-40460, and P2001-40461, both filed on Jul. 6, 2001, which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to optical fiber, and more particularly, to optical fiber that can prevent polarization variation for enhancing an optical efficiency, and a projection display of the same that can provide a high picture quality.
2. Background of the Related Art
In general, the optical fiber is a fibrous waveguide for transmission of a light widely used in optical communication, optical measurement, optical transmission, and the like.
A basic principle of the optical fiber is total reflection of a light. That is, a light passing through two media of different refractive indices refracts at an interface of the two media, when a relation as shown in an equation (1) comes into existence, which is called as Snell""s Law where n1, and n2 denote refractive indices of the two media, and xcex81 denotes an incident angle and xcex82 denotes a refraction angle.
n1 sin xcex81=n2 sin xcex82
That is, when the light progresses from a medium with a high refractive index to a medium with a low refractive index, there is a specific incident angle at which the refraction angle is 90xc2x0, and for an incident angle greater than the specific angle, the light is reflected at the interface of the two media, which is called as total reflection.
The optical fiber employs such a total reflection, and FIG. 1 illustrates a related art optical fiber.
Referring to FIG. 1, the related art optical fiber is provided with a core 11 in a central part, and a cladding 12 surrounding the core 11. For causing total reflection, the refractive index of the core 11 is made higher than the refractive index of the cladding 12. Therefore, the light incident to the core 11 progresses as the light is totally reflected along the core 11 according to a condition of the total reflection.
However, it is matter of course that the light progressing along the core 11 is involved in phase change, with a change a polarization direction. Particularly, when the optical fiber is stressed by bending, or heat, or an external pressure, the optical fiber is involved in change of the refractive index, with further change of the phase. Therefore, though the related art optical fiber transmits a photo energy effectively, the related art optical fiber has a problem in that the related art optical fiber changes a polarization direction. In application fields of the polarization, an effective use of the polarization light has been difficult due to a loss caused by the polarization change of the optical fiber.
In the meantime, for maintaining a fixed polarization direction, even a single mode optical fiber is employed. However, the single mode optical fiber is required to be thinner than a few xcexcm, has a limitation in a length thereof, and is susceptible to an external pressure or a stress caused by bending.
Meanwhile, as a display system for realizing a large sized screen, there is a projection display system in which a small picture is enlarged, and projected onto a large screen. Of the projection display systems, a projection display system employing a laser as a light source is under development, of which structure will be explained, briefly.
Referring to FIG. 2A, one exemplary related art projection display system is provided with a laser beam source 21 for emitting a laser beam, an illuminative optical system 22, a display panel 23, and an optical projection system 24. The display panel 23 displays a picture by controlling an amount of the laser beam in response to an electrical signal, and the picture is enlarged, and projected onto the screen 25 through the optical projection system 24.
Referring to FIG. 2B, another exemplary related art projection display system is provided with a laser beam source 31, an optical system 32, an AOM 33 for controlling a transmission amount of a laser beam in response to an electric signal related to a picture signal, a polygonal mirror 34 for providing a horizontal image by scanning the laser beam, and a galvanometer 35 for providing a vertical image by repetitive up and down rotation at a fixed angle. That is, the projection display system displays a picture on the screen 36 by rotation and angle combination of the galvanometer 35, and the polygon mirror 34.
The foregoing projection display system enhances clarity and reproducibility of colors, displays a picture with colors close to natural colors, and reproduces a clear picture quality as the picture has a high contrast.
However, the projection display system can not but have interference of the laser beam on the screen 25 or 36 caused by coherence of the laser beam, forming glittering speckles on the screen 25 or 36 coming from regular phases of the laser beam, that deteriorates picture quality, contrast, and resolution.
Accordingly, the present invention is directed to an optical fiber and a projection display system that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide an optical fiber for maintaining a polarization direction of an incident beam to enhance optical utilization efficiency.
Another object of the present invention is to provide a projection display system, in which a light utilization efficiency is enhanced by using the optical fiber, and speckles caused by laser beam interference is eliminated, for providing an excellent picture quality.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the optical fiber includes a core, a cladding surrounding the core, having a refractive index lower than the core, and PBS (Polarization Beam Splitter) layers in an incident part and emission part at opposite ends of the core, for transmission of a particular polarized beam.
The PBS layer is a multilayered thin film coated on the incident part, or the emission part, or a thin polarization plate bonded to the incident part, or the emission part. The PBS layers in the incident part and the emission part have the same polarization directions of transmissive laser beams.
Therefore, according to the present invention, the beam incident to the core through the PBS layer in the incident part can not pass the PBS layer in the emission part but reflected into the core even if a polarization direction thereof is changed by external causes in the middle. If this process is repeated, a beam having the same polarization direction with the incident beam emits through the PBS layer in the emission part. At the end, the polarization direction of the emitted beam becomes the same with the polarization direction of the incident beam, thereby enhancing an optical utilization efficiency.
In another aspect of the present invention, there is provided a projection display system including a beam source for emitting a laser beam of a polarization direction, an optical fiber for totally reflecting the laser beam to transmit the laser beam therethrough, and maintaining the polarization direction, vibration means connected to the optical fiber at least one or more than point, for vibrating the optical fiber, to vary a phase of the laser beam passing through the optical fiber, a display panel for controlling an amount of the laser beam from the optical fiber in response to an electric signal, to provide a picture, and a projection optical system for enlarging, and projecting the picture from the display panel onto a screen.
As explained, there are PBS layers in the incident part and the emission part of the optical fiber, for transmission of laser beams of the same polarization direction.
Thus, according to the present invention, when the vibration means applies vibration to the optical fiber, a phase of the laser beam becomes irregular. As a result, the laser beam interferes each other and the speckles are eliminated. In this instance, as has been explained, even if there may be a polarization loss caused by variation of the polarization direction of the laser beam, the PBS layers can secure an optical utilization efficiency higher than a certain level.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.